In general multiprocessing.Pool can interact quite badly with other, seemingly
unrelated, parts of a codebase due to Pool's reliance on fork. This method
cleans up all pools which are known to belong to Keras (and thus can be safely
terminated).

Args

grace_period

Time (in seconds) to wait for process cleanup to propagate.

use_sigkill

Boolean of whether or not to perform a cleanup pass using
SIGKILL.

Returns

A list of human readable strings describing all issues encountered. It is up
to the caller to decide whether to treat this as an error condition.